1. Field of the Invention
The invention relates to a friction ring for a synchronization unit of a switchable gear changing transmission. The invention relates also to a synchronization unit having a friction ring.
2. Discussion of Background Information
In synchronization units of a mechanical switchable gear changing transmission, e.g. in vehicle transmissions, friction rings serve to synchronize the relative speeds which occur between the gear wheel and the gear shaft during a gear change to one another. The synchronization is achieved in this respect by friction between the corresponding friction partners. The function of such transmissions and the process of the synchronization are known per se and no longer have to be explained in more detail to the person skilled in the art. Friction rings of synchronization units or other components of synchronization units have also been described in a versatile and detailed manner in the prior art.
EP 2 894 363 A1, for example, shows a generic friction ring. The friction ring comprises a conical friction ring body having an inner friction surface and an outer installation surface, wherein the inner friction surface extends at a predefinable friction angle and the outer installation surface extends at a predefinable installation angle conically along a friction ring axis. Due to the fact that the friction angle differs from the installation angle, an independent optimization of the functions “Synchronize” and “Separate” is possible. The friction ring body is formed as a segmented friction ring body which comprises a plurality of separate friction ring segments which form the friction ring body in a ring-shaped arrangement. EP 2 894 363 A1 shows also a friction ring body which consists of a single segment instead of a plurality of separate friction ring segments, wherein the friction ring body has a slit which is arranged perpendicular to the friction ring axis.
In the installed state the friction ring is positively connected to a conical synchronizer ring. In this respect the synchronizer ring has a conical inner installation surface which is formed corresponding to the outer installation surface of the friction ring. The friction ring is secured in the axial and radial direction to the friction ring axis via the conical inner installation surface of the synchronizer ring. Furthermore, securing mechanisms against rotation are provided at the friction ring ensuring that the friction ring is essentially connected also non-rotatably to the synchronizer ring, i.e. apart from little angular deflections occurring in a circumferential direction around the friction ring axis the friction ring is connected non-rotatably to the synchronizer ring.
In order to explain this friction ring reference is made in the following to the schematic FIG. 1a to FIG. 2 on the basis of which the prior art previously described will be described in more detail. In order to differentiate between the prior art and the present invention the reference numerals which refer to features of known examples are marked with an apostrophe, whereas the reference numerals which refer to features of examples according to the invention have no apostrophe.
In the following the friction ring is designated as a whole by the reference numeral 1′, the synchronizer ring by the reference numeral 2′ and the synchronization unit by the reference numeral 3′.
In a schematic representation the FIG. 1a and FIG. 1b show one and the same embodiment of a known segmented friction ring 1′. FIG. 1a shows the friction ring 1′ having a segmented friction ring body 4′ in an expanded configuration, whereas FIG. 1b shows the same friction ring 1′ in a compressed configuration. FIG. 1c shows a second embodiment of a known segmented friction ring 1′. For a better understanding FIG. 1d shows a section along the line I-I according to FIG. 1a or FIG. 1c, whereas FIG. 1e shows a section of the friction ring 1′ according to FIG. 1a or FIG. 1c in a perspective view.
As can clearly be recognized with reference to FIG. 1a and FIG. 1b, the friction ring body 4′ in this embodiment is a segmented friction ring body 4′ which comprises a plurality of separate friction ring segments 41′, 42′, 43′, in the present embodiment, that is, three friction ring segments 41′, 42′, 43′ which form the friction ring body 4′ in a ring-shaped arrangement. As it is shown in FIG. 1c, the friction ring body 4′ can also consist of a single segment 41′ instead of a plurality of separate friction ring segments. In this respect the friction ring body 4′ has one single separation area 5′ in the form of a slit which is perpendicular to a friction ring axis 6′. The slit has a width B′. Due to the slit a first separation surface 7′ and a second separation surface 8′ of the friction ring body 4′ are arranged at a distance from each other.
According to FIG. 1d the friction ring 1′ comprises a conical friction ring body 4′ having an inner friction surface 401′ and an outer installation surface 402′ which each bound the friction ring body 4′ in a radial direction extending perpendicular to the axial friction ring axis 6′. In this respect, the inner friction surface 401′ extends at a predefinable friction angle α1 and the outer installation surface 402′ extends at a predefinable installation angle α2, in each case conically along the friction ring axis 6′. Due to the fact that the friction angle α1 differs from the installation angle α2, an independent optimization of the functions “Synchronize” and “Separate” is possible.
As can be seen from FIG. 1e, a plurality of securing mechanisms against rotation 9′ or tabs are provided at the friction ring body 4′ which extend along the friction ring axis 6′. The securing mechanisms against rotation 9′ are arranged at the friction ring body 4′ in the circumferential direction U and engage in the installed state into corresponding tabs provided at the synchronizer ring 2′. The securing mechanisms against rotation 9′ ensure that the friction ring 1′ is essentially connected non-rotatably to the synchronizer ring 2′.
FIG. 2 shows an exploded diagram of a known synchronization unit 3′ comprising a friction ring 1′ and a synchronizer ring 2′. According to FIG. 3 the synchronization unit 3′ further comprises, in addition to the friction ring 1′ and the synchronizer ring 2′, in a manner known per se a sliding sleeve 10′ and a gear wheel 11′, wherein the aforesaid components are arranged coaxially to an axis 12′ of the synchronization unit 1′ such that the synchronizer ring 2′ can be displaced in the operating state by the sliding sleeve 10′ together with the friction ring 1′ along the axis 12′ in the direction towards the gear wheel 11′ so that the inner friction surface 401′ of the friction ring body 4′ can be brought into engagement with the gear wheel 11′.
Thanks to the use of the described segmented slitted friction ring some improvements have been made in practice.
Due to the fact that the friction ring is segmented, i.e. it has at least one slit, an expansion of the friction ring towards a bigger circumference of the ring is possible. And that is indispensable for avoiding the self-locking effect at the inner friction surface of the friction ring. Thanks to this fact the gear-shifting quality has been essentially improved.
But it has also become evident that even this improved friction ring which has proven itself in practice in the meantime can be further improved.
A major disadvantage of the slitted friction ring is that due to its arrangement in the axial direction relative to the synchronizer ring the friction ring cannot be clearly positioned. The friction ring can be deformed elastically by applying low forces in such a way that the slit closes until both separation surfaces touch each other. This includes a reduction of the circumference of the friction ring body with the result that the friction ring takes an uncontrolled axial position relative to the synchronizer ring during the synchronization. This uncontrolled axial position of the friction ring has a negative effect on the synchronizing process and thus on the gear-shifting quality.
Consequently, the outer installation surface of the friction ring and the inner installation surface of the synchronizer ring are unevenly used and thus worn. In order to counteract the wear of the installation surfaces caused hereby, a time-consuming, costly coating of the installation surfaces or the use of high-quality, expensive materials may be necessary.
A further disadvantage of the uncontrolled axial positioning of the friction ring relative to the synchronizer ring during the synchronization is that the synchronization unit is subject to increased mechanical load. This can, for example, lead to harmful vibrations or a higher shifting force and disrupts the reliability and accuracy of the synchronization. The cited effects are the more important the higher the synchronizing torque to be transmitted by the synchronization unit is.